Always read diff_view setting from the cookie

Prior, when the user had their view set to "parallel" and then visited a
merge request's changes tab _without_ passing the `view` parameter via
query string, the view would be parallel but the `Notes` class was
always instantiated with the default value from `diff_view` ("inline"),
resulting in broken markup when the form to add a line note was
dynamically inserted.

The cookie is set whenever the view is changed, so this value should
always be up-to-date.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14557 and https://gitlab.com/gitlab-org/gitlab-ce/issues/15285

See merge request !3732

Implement top navigation for profile area

Main idea is to keep left sidebar static so user is not confused by
changing context. Instead we put changing navigation with changing
content in one main block. I used profile area as a simplest way to 
implement and test this concept. Your feedback is welcome in comments

For https://gitlab.com/gitlab-org/gitlab-ce/issues/14354#note_4878536


Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !3824

Show project members only for members

fixes #5838 

See merge request !3752

Ci::Commit becomes a Pipeline object

1. Ci::Commit receives context: ref, :tag.
1. One Ci::Commit describes a one Pipeline
1. Pipeline is created from `.gitlab-ci.yml`
1. Pipeline is a ordered group of builds
1. We test MR against Pipeline
1. Pipelines have a separate view (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3703)
1. Pipeline can be triggered from UI (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3703)
1. Later we change `Trigger -> TriggerRequest -> Build` to `Trigger -> Pipeline` (future)
1. We add a Pipeline Hook that will be triggered on Pipeline status change  (future)
1. We extend notifications to use `Pipeline Hook` to send summary on pipeline changes (future)

After merging that I'll prepare a separate MR that will unify naming, database columns, table names:
```
Ci::Commit -> Pipeline
Ci::Build -> Build
CommitStatus -> Job
GenericCommitStatus -> ExternalJob

ci_commits -> pipelines
ci_builds -> jobs
```

This MR implements first 5 points.

This is made to solve this issue https://gitlab.com/gitlab-org/gitlab-ce/issues/14149.

See merge request !3653

Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix typos on sorting dropdown related to due date
Remove constant array and add Structs on Issue to keep due date data to fill options

Add due_date text field to sidebar issue#show
Add ability sorting issues by due date ASC and DESC
Add ability to filtering issues by No Due Date, Any Due Date, Due to tomorrow, Due in this week options
Add handling issue due_date field for MergeRequest
Update CHANGELOG
Fix ambigous match for issues#show sidebar
Fix SCREAMING_SNAKE_CASE offenses for due date contants
Add specs for due date sorting and filtering on issues

Mutliple label filter

Fixes #989 

See merge request !3438

Backport select_helper from EE



See merge request !3825